The present invention relates to a drive device for driving a display panel. More specifically, the present invention relates to a drive device of a display panel capable of applying a gradation voltage to a data line of a liquid crystal display panel according to an input video signal.
In a liquid crystal display panel of an active matrix type, a plurality of scanning lines is arranged to extend in a horizontal direction of a two-dimensional screen, and a plurality of data lines is arranged to extend in a vertical direction of the two-dimensional screen. Each of the scanning lines is arranged to cross each of the data lines. An electrode functioning as a pixel is disposed at a crossing point of each of the scanning lines and each of the data lines. Further, the liquid crystal display panel is provided with a drive device for applying a voltage to each of the data lines according to a brightness level indicated with an input video signal.
Patent Reference has disclosed a conventional drive device. The conventional drive device is configured to generate a voltage (referred to as a gradation voltage) for each gradient representing 64 scales of a brightness range that the input video signal can display. Then, the conventional drive device selects one of the gradation voltages corresponding to the brightness level indicated with the input video signal, and applies the gradation voltage to the data line.    Patent Reference: Japanese Patent Publication No. 2002-366115
In the conventional drive device disclosed in Patent Reference, a gradation voltage generation circuit is provided for inverting a polarity of the gradation voltage in a specific cycle, thereby preventing the liquid crystal display panel from deteriorating due to a problem such as burning out of the pixel. The gradation voltage generation circuit includes a switch for alternately switching between the gradation reference voltage with a positive polarity (VHP) and the gradation reference voltage with a negative polarity (VHN) in the specific cycle, so that the gradation reference voltage is applied to an input line of an amplifier. The amplifier amplifies the gradation reference voltage applied to the input line, so that the gradation voltage with the polarity switched in the specific cycle is generated.
In the conventional drive device described above, immediately after the gradation reference voltage with the positive polarity is applied to the input line of the amplifier, the input line is maintained at the voltage with the positive polarity. Similarly, immediately after the gradation reference voltage with the negative polarity is applied to the input line of the amplifier, the input line is maintained at the voltage with the negative polarity.
Accordingly, when the polarity of the gradation reference voltage is inverted, the gradation reference voltage with the negative polarity is applied to the input line of the amplifier maintained at the voltage with the positive polarity. Similarly, the gradation reference voltage with the positive polarity is applied to the input line of the amplifier maintained at the voltage with the negative polarity. As a result, immediately after the polarity of the gradation reference voltage is inverted, a temporary voltage variance is created on the input line of the amplifier. Accordingly, the voltage variance may have an influence on the gradation voltage to cause a ripple, thereby causing deterioration of an image displayed on the liquid crystal display panel.
In view of the problems described above, an object of the present invention is to provide a drive device capable of solving the problems of the conventional drive device. In the present invention, it is possible to invert a polarity of a gradation voltage without causing deterioration of an image.
Further objects and advantages of the invention will be apparent from the following description of the invention.